We once had a situation where we were flying quite a lot and not receiving any miles. Upon thorough investigation, it was discovered that the airline had, in some mysterious fashion, re-assigned our number to another person. Therefore, the miles were accruing into a holding space for miles flown by a person that doesn't "name-match" the account number listed upon their itinerary.

Needless to say, this was before we were Flyer Talk Junkies who checked our account obsessivly.

The only time I have seen this work is when a grandfather/father/son all had the same name and were able to pool miles. I also know of a couple of identical twin cases where the real frequent flyer "loaned" his/her ID to his/her twin-sib to garner the miles for the twin's random flights.